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  • 1
    Electronic Resource
    Electronic Resource
    Multinuclear magnetic resonance study of tautomerism in fluorinated β-diketones (1990)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 28 (1990), S. 645-650 
    Details
    ISSN: 0749-1581
    Keywords: 1H NMR ; 13C NMR ; 19F NMR ; β-Diketones ; Tautomerism ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Multinuclear NMR experiments on fluorinated β-diketones have furnished information on the various tautomers present in solution and their proportions. 2-Trifluoroacetyl-1-indalone in CDCI3 solution exists in the enol form, as a mixture of exocyclic and endocyclic cis-enols with the exocyclic form favoured, but in DMF-d7 solution the equilibrium shifts to 40% enol, 60% hydrate with the enol and hydrate being in slow exchange on the NMR time scale. 2-Trifluoroacetyl-1-tetralone in CDCI3 solution exists only as the enol forms, approximately equally populated, but in DMF-d7, unlike the indalone, no hydrate is formed although there is now 6% of the keto form present in slow exchange. The experimental results were compared with calculated data produced using molecular orbital simulations. These agree with the NMR results and predict that the tetralone enol tautomers are both significantly populated at room temperature but that the indalone exists primarily as the exocyclic enol. The oxygen-oxygen internuclear distance in the hydrogen bond was estimated from the OH proton chemical shift based on a calibration from solid-state data from model compounds, and agrees well with the predictions using the molecular mechanics approach.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260280716
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  • 2
    Electronic Resource
    Electronic Resource
    Conformation of ethane-1,2-diol from analysis of its NMR spectrum obtained using gradient-enhanced inverse detection (1993)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 31 (1993), S. 585-589 
    Details
    ISSN: 0749-1581
    Keywords: Ethanediol ; NMR ; Coupling constants ; Conformation ; Inverse detection ; Gradients ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 1H NMR spectrum of [13C]ethane-1,2-diol was measured at natural abundance using the 1H—13C inverse-detected HMQC method with magnetic field gradients. A limited solvent and temperature dependence study was undertaken and the vicinal 1H—1H coupling constants were related to those in model compounds. It is shown that the trans rotamer is significantly populated, in contradiction to some recent theoretical and experimental studies.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260310612
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  • 3
    Electronic Resource
    Electronic Resource
    Two-dimensional 1H—1H and 13C—1H maximum-quantum correlation NMR spectroscopy with application to the assignment of the NMR spectra of the bile salt sodium taurocholate (1995)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 33 (1995), S. 212-219 
    Details
    ISSN: 0749-1581
    Keywords: multiple quantum ; NMR ; two-dimensional ; taurocholate ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Following earlier studies on the development of one- and two-dimensional NMR methods based on selection of coherences via maximum-quantum pathways and using inverse 1H detection, a pulse sequence is now described for analogous direct heteronuclear detection for use in laboratories which do not have access to inverse detection technology. The method has been applied to the assignment of all of the 1H and 13C NMR resonances of sodium taurocholate, an important component of bile. The assignment of the resonances of major bile salts is important for the assignments of NMR resonances in bile itself to yield understanding of altered biochemistry in disease states. The effect of deliberately missetting the refocusing delay in the pulse sequence is shown to be beneficial in the assignment process.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260330310
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  • 4
    Electronic Resource
    Electronic Resource
    Tautomerism in 2-hydroxy-1-naphthaldehyde schiff bases in solution and the solid state investigated using 13C NMR spectroscopy (1993)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 31 (1993), S. 991-994 
    Details
    ISSN: 0749-1581
    Keywords: Schiff bases ; Tautomerism ; 13C NMR CP/MAS ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 13C and 1H NMR spectra of six Schiff bases formed from 2-hydroxy-1-naphthaldehyde and substituted anilines were measured and assigned in a variety of solvents. Based on the 13C chemical shifts and 3J(CH,NH), the ratio of the keto-amine and phenol-imine tautomers was derived using both 13C chemical shifts and 1H-1H coupling constants, the two methods giving comparable results. The solid-state 13C NMR spectra of two of these Schiff bases were also measured and interpreted. Based on chemical shift assignments from solution NMR, which showed a relationship between certain shifts and the proportions of the tautomers, it has been shown that these compounds exist essentially as the keto-amine form in the solid, the tautomer previously shown to be the more thermodynamically stable.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260311107
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  • 5
    Electronic Resource
    Electronic Resource
    A multinuclear magnetic resonance study of protonation in imidazo[1,2-a]pyrazine (1990)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 28 (1990), S. 874-877 
    Details
    ISSN: 0749-1581
    Keywords: NMR ; 13C ; 15N ; Protonation ; Imidazo[1,2-a]pyrazine ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1H and 13C NMR spectra are reported and assigned for imidazo[1,2-a] pyrazine and for N-1-methyl- and N-7-methyl-imidazo[1,2-a] pyrazinium iodides. The effect of protonation on the chemical shifts of the parent molecule is demonstrated, and through the use of 13C and 15N NMR spectra the site of protonation is deduced to be at N-1, in contrast to 2-aryl substituted compounds synthesised as potential cardiotonic agents where protonation occurs at N-7.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260281008
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  • 6
    Electronic Resource
    Electronic Resource
    Assessment of NMR probe temperature stability and gradient using a nematic phase solution (1994)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 32 (1994), S. 231-234 
    Details
    ISSN: 0749-1581
    Keywords: NMR probe ; Nematic phase ; Temperature stability ; Temperature gradient ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The measurement of the 1H NMR spectrum of a sealed sample of benzene dissolved in a nematic liquid crystal provides a convenient and sensitive test of both NMR probe temperature stability and of the temperature gradient across the sample.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260320408
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  • 7
    Electronic Resource
    Electronic Resource
    Studies of tautomerism and protonation in 2-aryl-1H-imidazo[1,2-a]imidazole derivatives using 1H and 13C NMR (1991)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 29 (1991), S. 1147-1151 
    Details
    ISSN: 0749-1581
    Keywords: Protonation ; Tautomerism ; NMR ; Imidazo[1,2-a]imidazole ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The tautomerism and protonation of the putative inotropic 2-(2′,4′-dimethoxy)phenyl-1H-imidazo[1,2-a]imidazole (2) has been studied in several solvents by comparing its 1H and 13C chemical shifts with those of its 1- and 7-methyl derivatives 3 and 4, respectively, and acid salts. Tautomer and rotamer populations were also estimated from measurements of proton relaxation rates and NOE effects. Heterocycle 2 exists predominantly as the 1H-tautomer in CDCl3, but as the 7H-tautomer in DMSO-d6 and methanol-d4-D2O solutions. In CDCl3 solution, 2 appears to exist with the N-1-H and 2′-OMe groups adjacent, but in DMSO-d6 the conformation is the rotated form with N-7-H and H-6′ adjacent; 3 exists as a mixture of rotamers in CDCl3 and in DMSO-d6 whereas 4 is in the form with the N-7-Me and H-6′ adjacent in both solvents. The observed conformational preferences have been compared with the results of semi-empirical molecular orbital calculations and found to be in broad agreement. Protonation of 2 occurs mainly at N-1 in DMSO-d6 and at N-7 in CDCl3, as expected from observed tautomeric ratios in the free base.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260291112
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  • 8
    Electronic Resource
    Electronic Resource
    Measurement of inter-proton distances from cross-relaxation rates determined by a selective null inversion-recovery NMR method (1992)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 30 (1992), S. 173-176 
    Details
    ISSN: 0749-1581
    Keywords: NMR ; Relaxation ; Selective pulses ; Distance ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An efficient method of measuring proton spin-lattice cross-relaxation rates in small molecules is proposed. The method involves measuring the difference in relaxation rates in a non-selective experiment and in one with all resonances except one of interest inverted. This procedure yields cross-relaxation rates between this nucleus and all other nuclei. These rates are independent of the effects of non-excited heteronuclei and of non-dipolar contributions and can be used to determine relative inter-proton distances. The method was tested using 7-azaindole and compared favourably with the standard NOE method for estimating proton proximities requiring less data acquisition time.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260300215
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  • 9
    Electronic Resource
    Electronic Resource
    Separation and characterization of components of peptide libraries using on-flow coupled HPLC - NMR spectroscopy (1995)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 33 (1995), S. 857-863 
    Details
    ISSN: 0749-1581
    Keywords: peptides ; HPLC-NMR ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The efficiency of directly coupled HPLC - NMR spectroscopy for the separation and characterization of synthetic peptide libraries was investigated using a model system based on a mixture of all 27 tripeptide combinations of alanine (A), methionine (M) and tyrosine (Y) as the C-terminal amides. The 1H NMR spectra were obtained in real time using on-flow HPLC - NMR spectroscopy at 600 MHz and 21 of the 27 peptides were identified on the basis of chemical shifts and coupling constants, including the use of diagnostic values derived from 1H NMR spectra and 1H—13C and 1H—15N HMQC studies on authentic A—A—A—OH and Y—Y—Y—OH. The effects on 1H NMR chemical shifts of pH and of varying proportions of acetonitrile and water as occurred during the gradient elution HPLC run were evaluated. The HPLC - NMR approach could provide a facile method for investigating the relative efficiency of resin-based peptide synthesis for different amino acid combinations and should rapidly provide data suitable for deriving structure-retention time relationships for peptides.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260331103
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